Conventionally, it is known to separate oil and water from the oil/water mixture using a floating oil collecting system (see Patent Documents 1 and 2). In such a floating oil collecting system, the oil/water mixture accumulated in storage tanks, such as a machine-tool coolant tank and a cleaning solvent tank, is sucked up with a pump, fed to a separation tank through an inflow pipe, so that the mixture may be separated into water and oil to be at a lower phase and an upper phase within this separation tank by the difference in specific gravity. The separated oil is collected through a discharge hose in a collecting container. The collected oil is suitably disposed of as waste fluid. The remaining liquid (water) where oil is removed is returned to the storage tank from the separation tank so as to be reused.
Further, it is conventionally known that a tip (suction inlet) of a suction hose of a pump is supported with a float apparatus in a storage tank, and the suction is carried out by floating the suction inlet at all times to follow a liquid level of the oil/water mixture in this storage tank (see Patent Document 1 and 2).